One type of accident involving tractor-trailer vehicles is caused when the manner of vehicle operation and/or road conditions result in changes in the dynamics of the vehicle causing the trailer to tip up on one side. The trailer will generally roll over starting at the rear and continuing to the front until the whole rig, including the tractor, is on its side. While it is possible that the operator may sense the lateral force acting on the trailer, the operator may not be aware of an incipient rollover condition; and, if the forces which caused this condition continue unabated, the operator may not be able to avoid the rollover.
In many instances, the tilting action normally preceding an actual rollover is greatest at the rear of the trailer. The rear set of wheels on the trailer may even leave the road for a short time without the operator being cognizant thereof. If the operator were made aware of excessive lateral forces occurring at the rear of the trailer, there might still remain sufficient time within which the tilting action can be countermanded by the operator reducing speed, applying brakes, increasing the turning radius of the vehicle, or other actions appropriate to reducing the lateral forces and prevent the tractor-trailer from rolling over. Of course, the lateral force conditions may arise so quickly, due to the manner of operation of the vehicle or external factors, that the operator may be unable to react even if immediately alerted to such conditions.
Prior art approaches to alleviation of the problem of sensing an impending rollover condition generally provide sensor means coupled to means for effecting remedial actions. In See et al U.S. Pat. No. 3,804,435, means were provided for protecting an operator and reducing possible injury in the event of a rollover particularly of a bulldozer which is frequently operated on steep hillsides where lateral tipping and rollover may be a considerable danger. Operator restraint means were combined with means responsive to the tilt angle of the vehicle beyond a predetermined angle for actuating the operation of the air bag restraint means. The tiltsensor taught was a conventional single pole, single throw mercury switch which completes a circuit from a power source to the valve means when the vehicle attains a predetermined angle with respect to the vertical. The angle is set at a point whereat the vehicle center of gravity just exceeds the pivot point which varies with different vehicles.
The system suggested by See et al is not intended for use in sensing the impending rollover conditions, but rather is directed to protecting the operator upon the occurrence of rollover. The combination suggested by See et al is not adapted for installation on a tractor-trailer rig and does not contemplate the dynamic lateral forces arising from the highway operation of trucks. Additionally, a warning to the operator in advance of rollover was not contemplated by See et al.
The approach offered by Eagle U.S. Pat. No. 4,592,565 provides relatively complex apparatus for detecting an incipient overturning moment in a vehicle which comprises position-controlling servomechanism means, centrifugal force measuring means which includes a pressure-to-electrical signal transducer for generating a pressure indicating signal depending on a centrifugal force acting on the vehicle in a generally lateral direction, pressure indicating signal to error signal conversion means coupled to an output of said transducer means and providing an error signal at its output, the servomechanism means accepting and amplifying the error signal for transmitting a position-controlling force related to the error signal to means for avoiding the incipient overturning moment to prevent turning over of the vehicle. Further, the Eagle disclosure also contemplates providing road-curvature indicating means for measuring the curvature of the road travelled on by the vehicle, speed-indicating means for measuring the speed of the vehicle and means to combine the two measurements to provide a signal indicative of an incipient overturning moment. This signal is transmitted to control servomechanism means operating upon the brake pedal, the acceleration pedal, and/or the steering wheel to reduce the incipient overturning moment prevent such overturning.